77 lines
2.8 KiB
Diff
77 lines
2.8 KiB
Diff
From a4d45e4dce8b5eccfdc372dec99b037447369ea8 Mon Sep 17 00:00:00 2001
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Thu, 7 Dec 2023 14:15:15 +0000
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Subject: [PATCH 112/196] printk: Adjust mapping for 32bit seq macros
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Note: This change only applies to 32bit architectures. On 64bit
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architectures the macros are NOPs.
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__ulseq_to_u64seq() computes the upper 32 bits of the passed
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argument value (@ulseq). The upper bits are derived from a base
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value (@rb_next_seq) in a way that assumes @ulseq represents a
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64bit number that is less than or equal to @rb_next_seq.
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Until now this mapping has been correct for all call sites. However,
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in a follow-up commit, values of @ulseq will be passed in that are
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higher than the base value. This requires a change to how the 32bit
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value is mapped to a 64bit sequence number.
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Rather than mapping @ulseq such that the base value is the end of a
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32bit block, map @ulseq such that the base value is in the middle of
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a 32bit block. This allows supporting 31 bits before and after the
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base value, which is deemed acceptable for the console sequence
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number during runtime.
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Here is an example to illustrate the previous and new mappings.
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For a base value (@rb_next_seq) of 2 2000 0000...
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Before this change the range of possible return values was:
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1 2000 0001 to 2 2000 0000
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__ulseq_to_u64seq(1fff ffff) => 2 1fff ffff
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__ulseq_to_u64seq(2000 0000) => 2 2000 0000
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__ulseq_to_u64seq(2000 0001) => 1 2000 0001
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__ulseq_to_u64seq(9fff ffff) => 1 9fff ffff
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__ulseq_to_u64seq(a000 0000) => 1 a000 0000
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__ulseq_to_u64seq(a000 0001) => 1 a000 0001
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After this change the range of possible return values are:
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1 a000 0001 to 2 a000 0000
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__ulseq_to_u64seq(1fff ffff) => 2 1fff ffff
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__ulseq_to_u64seq(2000 0000) => 2 2000 0000
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__ulseq_to_u64seq(2000 0001) => 2 2000 0001
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__ulseq_to_u64seq(9fff ffff) => 2 9fff ffff
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__ulseq_to_u64seq(a000 0000) => 2 a000 0000
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__ulseq_to_u64seq(a000 0001) => 1 a000 0001
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[ john.ogness: Rewrite commit message. ]
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Reported-by: Francesco Dolcini <francesco@dolcini.it>
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Reported-by: kernel test robot <oliver.sang@intel.com>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/printk/printk_ringbuffer.h | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
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index b82a96dc2ea2..12f60c782e46 100644
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--- a/kernel/printk/printk_ringbuffer.h
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+++ b/kernel/printk/printk_ringbuffer.h
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@@ -407,7 +407,7 @@ static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq)
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* Also the access to the ring buffer is always safe.
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*/
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rb_next_seq = prb_next_seq(rb);
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- seq = rb_next_seq - ((u32)rb_next_seq - ulseq);
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+ seq = rb_next_seq - (s32)((u32)rb_next_seq - ulseq);
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return seq;
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}
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--
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2.43.2
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